Bump to latest pom-imagej

Updates to pom-imagej 2.16 to get the latest version of dependencies.
Add Open and SaveDataset

Migrated from imagej-common. These are stand-alone commands and belong
in this component.
SaveDataset: convert to trivial SaveAsImage

For now, SaveDataset wasn't really intended to do anything beyond what
SaveAsImage already does. So let's make it a trivial extension, but it
still fulfills the role of providing a File > Export > Image... command.